Who's speaking? linkd.in/jbaruch. stackoverflow.com/users/402053/jbaruch

Transcription

1

2 Who's speaking? linkd.in/jbaruch stackoverflow.com/users/402053/jbaruch

3 Frogs Groovy

4 Frogs Groovy Hosting Groovy on Bintray Hosting Groovy on Artifactory Bintray UI is Grails Artifactory plugins are Groovy Gradle and Grails plugins on Bintray

5 First Season Was a Blast!

6

7 BTW,

8 1. Two entertaining guys on stage

9

10 1. Two entertaining guys on stage 2. Funny Puzzling questions 3. You think and vote 4. Awesome Groovy t-shirts fly in the air 5. Official twitter handle! groovypuzzlers

11

12 Cédric?!

13 All works (or doesn't work) in Groovy 2.4.5

14

15

16 'a'..'z'.each { println it } A. a b c... z B. NoSuchMethodError C. z D. Won t run

17

18 ('a'..'z').each { println it } You knew it, right?

19 All problems in computer science can be solved by another pair of parentheses John McCarthy, the inventor of LISP

20 And the t-shirt goes to

21

22 How Many Bachs? def back = 'back' def quotes = ["I'll be $back", "I'll be ${-> back}", "I'll be ${back}", A.No Bachs "I'll be "+back] println quotes back = 'Bach' B.One Bach println quotes C.Two Bachs D.Three Bachs

23

24 Only closures are evaluated at runtime Others are inlined

25 Only closures are evaluated at def back = 'back' def quotes = ["I'll be $back", "I'll be ${-> back}", "I'll be ${back}", "I'll be "+back] runtime Others are inlined

26 Only closures are evaluated at def back = 'back' def quotes = ["I'll be $back", "I'll be ${-> back}", "I'll be ${back}", "I'll be "+back] runtime Others are inlined That is the only closure

27 And the t-shirt goes to

28

29

30 How one prints 666? A. def beast = '6' * Math.PI B. def beast = '6' * '3' C. def beast = '667' 1 D. def beast = '6' + '6'

31

32 def beast = '6' * Math.PI

33 def beast = '6' *

34

35 /** * Repeat a String a certain number of times. * self a String to be repeated factor the number of times the String should be repeated a String composed of a repetition IllegalArgumentException if the number of repetitions is < */ public static String multiply(string self, Number factor) { int size = factor.intvalue(); }

36 def beast = '6' *

37 def beast = '6' * 3

38 Pop Quiz! B. def beast = '6' * '3' C. def beast = '667' 1 D. def beast = '6' + '6'

39 Pop Quiz! B. def beast = '6' * '3' C. def beast = '667' 1 D. def beast = '6' + '6' + (0 + 6)

40 Pop Quiz! B. def beast = '6' * '3' C. def beast = '667' 1 D. def beast = '6' + '6' + (0 + 6) Yup, I am watching you!

41 And the t-shirt goes to

42

43 class THERE_CAN_BE_ONLY_ONE { } class MacLeod { } THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class clazz = THERE_CAN_BE_ONLY_ONE return clazz.newinstance() } println new MacLeod().THERE_CAN_BE_ONLY_ONE

44 class THERE_CAN_BE_ONLY_ONE { } class MacLeod { THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class clazz = THERE_CAN_BE_ONLY_ONE return clazz.newinstance() } } println new MacLeod().THERE_CAN_BE_ONLY_ONE A. Won't start B. No such property: THERE_CAN_BE_ONLY_ONE for class: MacLeod C. THERE_CAN_BE_ONLY_ONE@3d74bf60 D. Another Exception

45

46 A.MultipleCompilationErrorsException B.StackOverflowError C.NullPointerException D.Yet Another Exception

47

48 class MacLeod { } THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class clazz = THERE_CAN_BE_ONLY_ONE return clazz.newinstance() }

49 class MacLeod { } THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class clazz = getthere_can_be_only_one() return clazz.newinstance() }

50 Let's Fix It! Class<THERE_CAN_BE_ONLY_ONE> clazz = THERE_CAN_BE_ONLY_ONE.class

51 class MacLeod { } THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class<THERE_CAN_BE_ONLY_ONE> clazz = THERE_CAN_BE_ONLY_ONE.class return clazz.newinstance() }

52

53 class MacLeod { } THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class<THERE_CAN_BE_ONLY_ONE> clazz = getthere_can_be_only_one().class return clazz.newinstance() }

54 Let's Fix It! Class<THERE_CAN_BE_ONLY_ONE> clazz = (THERE_CAN_BE_ONLY_ONE as Class)

55 class MacLeod { } THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class<THERE_CAN_BE_ONLY_ONE> clazz = (THERE_CAN_BE_ONLY_ONE as Class) return clazz.newinstance() }

56

57 class MacLeod { } THERE_CAN_BE_ONLY_ONE getthere_can_be_only_one() { Class<THERE_CAN_BE_ONLY_ONE> clazz = (getthere_can_be_only_one() as Class) return clazz.newinstance() }

58 Let's Fix It!

59 And the t-shirt goes to

60

61 @groovy.transform.inheritconstructors class TreaayeMap extends HashMap { } TreaayeMap a = [5] TreaayeMap b = [6] println "${a.getclass()} ${a.equals(b)}" A.class HashMap true B.class TreaayeMap false C.class TreaayeMap true D.class HashMap false

62

63

64

65 TreaayeMap a = [5]

66 TreaayeMap a = [5]

67 TreaayeMap a = [5]

68 TreaayeMap a = class TreaayeMap extends HashMap { }

69 /** * Constructs an empty <tt>hashmap</tt> with the specified initial * capacity and the default load factor (0.75). * initialcapacity the initial capacity. IllegalArgumentException if the initial capacity is negative. */ public HashMap(int initialcapacity) TreaayeMap a = class TreaayeMap extends HashMap { }

70 equals() doesn t care about capacity, mappings only

71 And the t-shirt goes to

72

73 class Kitty { def fur } def kitties = [new Kitty(fur: 'soft'),new Kitty(fur: 'warm'),new Kitty(fur: 'purr') ] println kitties.collect { it.fur } println kitties*.fur println kitties.fur How many of the printed lines will be the same? A.All different B.2 similar, one different C.All the same

74

75 class Kitty { def fur } def kitties println kitties.collect { it.fur } println kitties*.fur println kitties.fur How many of the printed lines will be the same? A.All different B.2 similar, one different C.All the same

76

77 class Kitty { def fur } def kitties println kitties.fur

78 class Kitty { def fur } def kitties println kitties.fur

79 class Kitty { def fur } def kitties println kitties.collect { it.fur }

80 class Kitty { def fur } def kitties println kitties.collect { it.fur } public static Collection ascollection(object value) { if (value == null) { return Collections.EMPTY_LIST; } }

81 class Kitty { def fur } def kitties println kitties*.fur

82 class Kitty { def fur } def kitties println kitties*.fur

83 class Kitty { def fur } def kitties println kitties*.fur

84 Consistency, yeah. [] null Caught: java.lang.nullpointerexception: Cannot get property 'fur' on null object

85 All happy families are alike; each unhappy family is unhappy in its own way. Leo Tolstoy, Anna Karenina

86 And the t-shirt goes to

87

88 ArrayList<String> expendables = ['Arnold', 'Chuck', Sly'] def expendable = //someone from the list for(string hero in expendables) { if(hero == expendable){ expendables.remove(hero) } } println expendables

89 Which one won t cause a ConcurrentModificationException? ArrayList<String> expendables = ['Arnold', 'Chuck', Sly'] def expendable = //someone from the list for(string hero in expendables) { if(hero == expendable){ expendables.remove(hero) } } println expendables A.Can't avoid CME B.Arnold C.Chuck D.Sly

90

91

92 You have been warned.

93 Let s decompile this, baby! List expendables = Arrays.asList(new String[]{"Arnold", "Chuck", " Sly"}); String expendable = "Chuck"; Iterator iterator = expendables.iterator(); while(iterator.hasnext()) { String hero = (String)iterator.next(); if(hero.equals(expendable)) { expendables.remove(hero); } }

94 while(iterator.hasnext()) { String hero = (String)iterator.next(); if(hero.equals(expendable)) { // expendables.remove(hero); } }

95 while(iterator.hasnext()) { String hero = (String)iterator.next(); if(hero.equals(expendable)) { // expendables.remove(hero); } } public E next() { checkforcomodification(); cursor = i + 1; } public boolean hasnext() { return cursor!= size(); } Modifications are only checked in the next cycle Getting ready for hasnext() check in the next cycle Exit on last element +1 == size()

96 while(iterator.hasnext()) { String hero = (String)iterator.next(); if(hero.equals(expendable)) { // expendables.remove(hero); } } public E next() { checkforcomodification(); cursor = i + 1; } After Sly cursor is 3 public boolean hasnext() { return cursor!= size(); } And size is 3 as well All good. Now let s mess with

97 while(iterator.hasnext()) { String hero = (String)iterator.next(); if(hero.equals(expendable)) { expendables.remove(hero); } } public E next() { checkforcomodification(); cursor = i + 1; } public boolean hasnext() { return cursor!= size(); } After Chuck the cursor is 2 Then we remove the element And now the size now is 2! It won t get to the next() to run

98 Hey, what about me?!

99 while(iterator.hasnext()) { String hero = (String)iterator.next(); if(hero.equals(expendable)) { expendables.remove(hero); } } public E next() { checkforcomodification(); cursor = i + 1; } After Sly the cursor is 3 public boolean hasnext() { return cursor!= size(); } Then we remove the element But the size now is 2! It will go to another loop and fail on

100 And the t-shirt goes to

101

102 String truth = 'false' boolean groovytruth = truth println groovytruth

103 String truth = 'false' boolean groovytruth = truth println groovytruth A.false B.true C.ClassCastException D.Startup error

104

105

106

107 And the t-shirt goes to

108

109 assert 1L == 1 println 1L.equals(1) A. Assertion failed B. true C. false D. MissingMethodException

110

111

112

113

114 And the t-shirt goes to

115

116

117 A. [[2, 3, 5], [2, 4, 8], [42, 73, , 0]] B. Won't run C. [[null, null, null, 5]] D. null

118

119

120

121 No t-shirt for this guy

122

123 def jailhouserock def lovemetender def rockaroundtheclock = [1,2,3] jailhouserock?:[] + lovemetender?:[] + rockaroundtheclock?:[] *Yes, we know, it's not Elvis' song.

124 def jailhouserock def lovemetender def rockaroundtheclock = [1,2,3] jailhouserock?:[] + lovemetender?:[] + rockaroundtheclock?:[] A.[null] B.null C.[] D.[1,2,3]

125

126 def jailhouserock def lovemetender def rockaroundtheclock = [1,2,3] jailhouserock?:[] + lovemetender?:[] + rockaroundtheclock?:[]

127 def jailhouserock def lovemetender def rockaroundtheclock = [1,2,3] jailhouserock?:[null]?:[] + rockaroundtheclock?:[]

128 def jailhouserock def lovemetender def rockaroundtheclock = [1,2,3] jailhouserock?:[null]?:[1,2,3]?:[]

129 def jailhouserock def lovemetender def rockaroundtheclock = [1,2,3] [null]

130 Let's fix it (jailhouserock?:[])+(lovemetender?:[])+(rockaroundtheclock?:[]) Love me tender!

131 And the t-shirt goes to

132 Conclusions

133 1. Write readable code 2. Comment neat tricks 3. Sometimes it is just a bug 4. Use static code analysis (intellij IDEA!) 5. Rtfm 6. Parentheses. Always use Parentheses.

134 We keep going! (Look at the awesome t-shirts!) Puzzlers? Gotchas? Fetal position inducing behavior? - puzzlers jfrog.com - Groovypuzzlers

135 Jfrog always pays its debts

136 Positive feedback? Fill the feedback form! Praise us on twitter groovypuzzlers - Groovypuzzlers - tlberglund - jbaruch Negative feeback? /dev/null

137 No, Thank you!